In 820, about two centuries after Vinitaruci, a Chinese Buddhist monk known as Wu Yantong (Vo Ngon Thong in Vietnamese) came to live in the Kien So pagoda located in the village of Phu Dong, Bac Ninh province (present-day Ha Bac). He was to become the founder of the second Chan sect in Vietnam. He was born in Guangzhou with the family name Zheng. He later studied at the Shuanglin ("double forest") pagoda in Yuzhou, China. According to some sources, Yuzbou was then part of Zhejiang province. To others, it belonged to Guizhou and was the main town of the Weichuan district. Following the fall of the Tang dynasty, Yuzhou became known as Sizhou. Although very learned, Wu Yantong was said to be a reserved man (e.g., the Chinese monograph Chuan Deng Liu referred to him as Bu Yutong, or "not through spoken language"). The following story is recounted in Thien Uyen Tap Anh:

Bai Zhang (Vietnamese: Bach Truong) (710-814), originally from Changluo in Fuzhou, was Ma the Patriarch’s favorite disciple. After finishing his studies under Ma, he went to cloister himself in Da Hong mountain, near Fuzhou. He owed his name to the height of the mountain where he retired, for Bai Zhang means "one hundred paces". According to the Chinese Chuan Deng Liu (Truyen Dang Luc), Bai Zhang founded two Chan sects in China, the Thien Quy Nguong and Thien Lam Te sects. In fact, Bai Zhang was also at the origin of another sect, the Wu Yantong sect, this time in Vietnam, not China. To understand the conceptual basis of the Wu Yantong sect which concerns us here, we must first have a firm grasp of Bai Zhang’s philosophy.

The fundamentals of his philosophy can be inferred from this conversation between Bai Zhang and some of his disciples. One day, during a lesson, a disciple asked Bai Zhang about the Buddhist concept of corruption expressed in the scriptures. He answered:

The Chuan Deng Liu, which reports this conversation, adds that after hearing the master’s explanation, Wu Yantong had a deep religious experience, went back to Guangzhou and secluded himself in the An Hoa Pagoda. (Thien Uyen Tap Anh refers to it as the Hoa An Pagoda). The fundamental concept of Bai Zhang’s philosophy is a state of absolute abstinence called the "no-thinking" position. One is absolutely at peace, free from interminable, disorderly thought and feeling in the mind and heart. Then one’s spirit may blaze and reality will appear clearly before one’s eyes. That is enlightenment and deliverance. That is Nirvana. This is the nature of Bai Zhang’s teachings which were to be spread in Vietnam through the Wu Yantong sect.

In the year 820, Wu Yantong went to Vietnam and came to the Kien So Pagoda in Phu Dong (Bac Ninh province). All day long he sat, facing the wall, without pronouncing a word. He sat like this for several years, without anyone knowing who he was. Only the resident monk of that Pagoda, named Cam Thanh, knew that he was a high-ranking monk in his Buddhist order, and served him with devotion.

In 826, Wu Yantong died, passing his Buddhist seal to Cam Thanh. Before dying he spoke to Cam Thanh:

When he had taught this, Wu Yantong clasped his hands and died. Cam Thanh incinerated his body, gathered the remains and built a tower on Tien Son mountain. Wu Yantong died at the age of 98, in the year of the horse (826).

The litany recorded above and attributed to Huairang (677-714) is an important scripture, as this monk was the direct disciple of the sixth Patriarch of the Chinese Chan sect, Hui Neng, and the most famous one as well. Huairang became Ma Daoyi’s teacher, who was later to be Bai Zhang’s. Finally Bai Zhang passed his knowledge lo Wu Yantong .

Let us delve a bit into the significance of this litany. The last two lines express a warning: "If not in presence of higher intelligence, prudence in words." If the interlocutor is not a highly intelligent, educated man, one must not communicate the content of this litany. Why was such a warning necessary? Was it because the depth, the power of these words was beyond the simple man’s understanding?

How do we understand the first four lines according to Wu Yantong’s and Huairang’s philosophy? Knowledge is in nature, all events: all phenomena in the universe appear to make up reality, but in fact they are dependent on the activity of consciousness to subsist and maintain themselves. This is the mysterious truth that the simple man is unable to believe or understand. If through training, a person succeeds in ending consciousness, reaching the state called "no thinking", without thought, consciousness or differentiation, then all knowledge, all things, all phenomena lose their support, are unable to live or become reality. It is then that real enlightenment comes, that the intelligence blazes forth. The religious person receives enlightenment and deliverance; all obstacles are swept away.

Reality exists before us, but distorted, disfigured by the will of the heart that tries to differentiate things. That propensity to differentiate is our ordinary conscious state. Religious training aims at mastering this will to make way for the illumination of the intelligence. In Buddhist writings this is called Prajna’s intelligence, a state of perfect understanding. In the light of Prajna’s intelligence, the world we perceive before us is not the everyday world, but the reality, the world of Nirvana.

According to Thien Uyen Tap Anh, the Wu Yantong order spanned 15 generations. Only the first four are of concern to us here, the rest will be dealt with in a following chapter (Buddhism under the Ly).

1. Wu Yantong (died 826)

2. Cam Thanh (died 860)

3. Thien Hoi (died 900)

4. Van Phong (died 959)

The Wu Yantong Chan sect differs from Vinitaruci in several respects. Though both sects were introduced from China, the Vinitaruci sect was established in Vietnam by an Indian monk and betrays the influence of Indian Buddhism, while the Wu Yantong order was founded after Hui Neng, the sixth patriarch, and therefore carries the mark of Chinese Buddhism. Bai Zhang followed three generations after Hui Neng in a direct line, and was to become Wu Yantong ‘s teacher. He wrote a well-known series of books titled Bach Truong Thanh Quy which lay down the laws regulating the activities and training of monks in religious institutes. It is quite possible that Wu Yantong himself introduced these regulations into Vietnamese pagodas. The aim of this set of rules was to create a stable routine in training and daily activities, thus aiding monks to achieve tranquillity in their hearts.

The fundamental idea in the Wu Yantong system is that the truth is not far from us, it is before us, in every man himself. Truth can only be perceived directly and cannot be understood through the medium of language, written texts, books. When speaking about prompt enlightenment, we mean that there is no need of language, written texts or any speculation.. Here we should associate these thoughts with a statement by Bai Zhang, typical for South China Chan sect: "If the heart is void, the intellect will blaze itself’. What does the word "void" mean? At a low level, it means to have no evil deed or thought, to have no trivial and vulgar ambition. At a higher level, it means something superior than language, thought and speculation. The consciousness seems to stop and does not run after any inside or outside predestined fates.

Later on, several authors, basing themselves on this text, went on to explain it as "prompt" enlightenment. Such an explanation does not conform to the fundamental thought of Chan Buddhism in general, and not only Hui Neng’s Chan sect in particular. It should be understood as a direct (and not prompt) enlightenment.

Let us recall the litany said to be written by Bodhidharma, which summarizes the guiding principles of Chan Buddhism as follows:

To train the heart to become Buddha.

If we do not refer to texts for explanation, but base ourselves instead on the intent of the litany, we understand that the fundamental idea is that truth is not far from us, but is in every person’s heart, that we can find Truth in that heart by apprehending it directly without the help of language, texts, books or teaching. Basically, one cannot grasp Truth in words, not even through the classical prayers or a master’s teachings, nor even by one’s own power of reason. Truth must be met directly. In fact the crux of the matter is not whether it takes a short or long time to reach this point but whether one approaches it directly or indirectly. If indirectly, then Truth will remain forever far from us; if directly, then Truth appears right in front of us.

The aim is not only to deliver mankind from suffering and the cycle of reincarnation, but also rather to reach Truth as an end in itself. It is necessary, however, that you know to look into yourself to find the truth that resides in your soul, your heart. If you search for truth around you, you will pass from Karma to Karma without reaching enlightenment and deliverance. The ocean of suffering will only widen and the shores of enlightenment remain distant and dark

Nguyen Hoc (died 1175), also a patriarch of the fourth generation of the Wu Yantong order, tried to clarify these precepts in the following verses:

These lines express the fundamental beliefs of Vietnamese Buddhism, and of Buddhism in general.

Cam Thanh was born in Tien Du district. While his original name remains unclear, we do know that he first took the name Lap Duc upon entering the orders. A notable in the village, by the name of Nguyen, built a pagoda and asked him to become the resident monk. He at first refused, but then, according to Thien Uyen Tap Anh, he had a dream, in which an angel advised him to accept the offer, for not long thereafter he would benefit greatly from it. He therefore accepted. The pagoda was called Kien So, located in Phu Dong, Tien Du (former Bac Ninh province).

Nanyue Huairang was the first to receive this heart to heart teaching; Huairang taught Ma Daoyi in the same way, and he in turn became Bai Zhang’s teacher. It is from Bai Zhang that I know this method. It is by now well known in the North. Since there are many men who follow the way of Mahayana, I decided to go South to seek men of intellect: A predestined cause ordained our meeting".

Then Wu Yantong taught his disciple a litany, which we divide into several parts and paraphrase, in the interest of clarity.

a. History of Buddhism. The first section of the poem recalls the legendary history of the faith, beginning from Sakyamuni, passing through Mahakasyapa and so on, until Bodhidharma brought it to China and founded Chinese Chan Buddhism. Thereafter, Chan Buddhism was divided into five sects. The first Chan order is known as the "heart sect", since it postulates the heart which is in every living creature as its fundamental principle.

b. The principle of the heart. To say that Buddha transmitted the religion of the eyes to his disciple Mahakasyapa is in fact to say that Buddha transmitted nothing at all, because genuine religion is nothing more than the heart that resides already within Mahakasyapa as it does in every person. If we can attest to the existence of the heart, we can also be sure that the Western Paradise, Buddha’s universe, the Nirvana, is always to be found in that heart and nowhere else. The same moon, the same sun, the same mountains and rivers fill this world, so if we can attest to the existence of the heart, then the same moon, sun, mountains and rivers can be said to constitute Nirvana. One must follow this Truth exactly, for the slightest error will cause a deviation of a thousand miles. Indeed, Truth is within everyone, and the farther one goes searching for it, the farther one is from the Truth.

c. Wu Yantong enjoined Cam Thanh to observe carefully, think deeply and not misunderstand the spirit of his teaching, as any misunderstanding might lead future generations into error. The marvelous heart, i.e. Nirvana, cannot be asked about directly, because it is above reason, above language. Thus if anyone asks about it, one must keep silent.

Thien Hoi was born in Sieu Loai district, Bac Ninh province (actual Ha Bac). As a boy, he studied at the Dinh Thien Pagoda in his native village. While still an adolescent he entered orders and took the name To Phong. He then became a disciple of Cam Thanh in Kien So Pagoda.

One day the disciple asked his teacher, Cam Thanh, "In the sutras, Gautama Buddha said he trained in the immensity and void to become a Buddha. Now you say the heart is Buddha. Buddha is the heart: "What do you mean by this?" The master answered, "Who is the person speaking the words spoken in the sutras?"

"Those words were not pronounced by the Buddha then?"

"No, Buddha did not speak those words. In the Scriptures, Buddha says, "when I was among the living, I taught them for 49 years, without ever writing down a single sentence". This he said because his religion was the true one. If you rely upon written texts to find the way, you will become bogged down in details; if you endure suffering to find Buddha you will become lost; if you part with the heart to find Buddha, you commit a heresy; but if you accept that this heart is Buddha then it must be so."

The disciple asked, "If you say the heart is Buddha, then within the heart what is Buddha and what isn’t?"

"If that is so, I understand."’

"What have you understood?"

"That Buddha is everywhere, in everything and where Buddha is, there also is the heart."

Once he had spoken, the disciple prostrated himself. Cam Thanh said, "So you have achieved enlightenment." He then gave his disciple the name Thien Hoi, which means "to understand well". The latter returned to Dinh Thien Pagoda to become the resident monk there. In the year 800 he died, passing his seal to his disciple, Van Phong. Between the introduction of Buddhism in Vietnam and the founding of the Wu Yantong sect lies a period of almost one thousand years. Vietnam was during this time known successively as Giao Chi, Giao Chau, Ai Chau, Nhat Nam. It was already one of the bases from which Buddhism was to spread through East Asia, one of the earliest locales where Buddhist sutras were preached and translated, and finally one of the important stops for monks teaching and searching for scriptures.

Whether originating from the South or the North the proselytizing of Buddhism was always peaceful and showed no sign of xenophobia towards foreign religions, as was the case in China. Many Vietnamese came to Buddhism of their own accord, and adopted the Buddhist beliefs such as compassion, reincarnation, retribution, etc., in order to train themselves and help others. There were some (such as Ly Phat Tu) who used Buddhism to rally the population to resist the domination of the Chinese. In time, Buddhism penetrated deeper and deeper into the heart of the Vietnamese people. By the end of Chinese rule, it had become generalized throughout the society. In every Vietnamese Buddhist, religious identity and national identity were closely related, and became strong factors in the national insurrection of the tenth century. This mixed identity also created favorable conditions for the adoption of Buddhism as a national religion after the recovery of Vietnam’s independence.